A variety of polymeric materials are used in film applications. In particular, low density polyethylene (LDPE) produced by high pressure free radical polymerization, and linear low density polyethylene (LLDPE) produced by Ziegler-Natta-catalyzed polymerization, have been used, as well as high density polyethylene (HDPE) produced by a variety of polymerization methods. The lower density materials are typically crosslinked to improve various properties such as mechanical strength, processability, and resistance to high temperature degradation.
Crosslinked LDPE offers a number of advantages over crosslinked LLDPE. In particular, LDPE has better processability characteristics, such as lower melt fracture, higher melt strength, and reduced torque requirements in extrusion. However, uncrosslinked LLDPE can provide less than satisfactory film properties, unless processing aids are added. Indeed, even certain crosslinked LLDPEs can be insufficient for some film applications.
There remains a need in the art for grafted and crosslinked polymer compositions which combine the processability advantages of LDPEs and LLDPEs and the mechanical strength and other superior film properties of HDPEs.